South Korea says the suspicious powder found in a threatening letter sent to Seoul's defense minister has been found to be flour.
Investigators earlier Tuesday said they were investigating the letter as an attempted act of terror against Defense Minister Kim Kwan-jin.
They said the letter is similar to the hundreds of leaflets found scattered last week near the defense ministry that threatened to "punish" Kim for what it said was his tough stance on North Korea.
The North has repeatedly threatened to attack the South because of the annual U.S.-South Korean military drills and United Nations sanctions that were passed in response to its February nuclear test.
Pyongyang has gradually reduced its harsh war rhetoric in recent days. Last week, it outlined the conditions it said were necessary to engage in dialogue with Washington, but insisted it will not abandon its nuclear program.
Many analysts say there is no evidence North Korea intends to follow through on its threats of missile attacks and nuclear war. But Seoul has recently blamed the North for a computer attack last month that shut down thousands of computers at South Korean banks and broadcasters.
The two countries have been in a technical state of war for more than 60 years. The agreement that ended the 1950 to 1953 civil war hostilities was only a truce.